Aircraft hydraulic systems may be driven by one or more sources. For example, referring to FIG. 1, output hydraulic power may be provided by engine driven sources 102 or (104) electric motor driven sources 106. In the event of failure of unavailability of the engine driven sources (e.g., pumps) 102, the hydraulic power may be provided by the electric motor driven sources (e.g., pumps) 106. The engine driven sources 102 and the electric motor driven sources 106 may, in turn, be driven by other engines referred to in FIG. 1 as “main engines.”
In order to provide an alternate source of electric power (e.g., in the event that the main engines fail or are unavailable), a Ram Air Turbine (RAT) may be included. In some instances (e.g., under some flight conditions), the RAT might not provide sufficient power to start the electric motor driven sources/pumps 106. For example, the electric motor driven sources 106 may impose high current inrush and breakaway torque requirements at turn-on. As a result, an overload condition imposed on the RAT can have adverse effects on an emergency electric system, and may result in a loss of hydraulic power on the aircraft. Alternatively, the RAT could be sized to provide sufficient power, however doing so would result in additional weight being added to the aircraft.